1. Field of the Invention
This invention relates to an image forming apparatus having a document feeder which transports a document while prefeeding the next document.
2. Description of the Related Art
An automatic document feeder generally consists of a document feeding unit which feeds documents on a document feed tray one by one, a document transporting unit having a conveyor belt which transports a document fed from the document feeding unit to a predetermined exposure location on a platen glass, and a document discharging unit which discharges a document transported from the document transporting unit onto a document discharge tray. A known document feeding unit comprises a feeding roller which feed a document on the tray, and a resist unit which stops a fed document to correct the skew of the document.
In such an automatic document feeder, when a copy operation is started, a document which has been fed out from the document feed tray is temporarily stopped at the resist unit, and then transported to the predetermined exposure location on the platen glass. On the other hand, during when this document (previous document) is transported onto the platen glass, the next document is fed to the resist unit and is stopped while being formed into a loop. Then, the control is performed so that the next document is transported onto the platen glass at the same time when the copy operation of the previous document is finished and the previous document is discharged to the document discharging unit. When a trouble such as a jam arises in the main body of the copying apparatus during an operation of copying a plurality of documents, both the drive operations of the main body and the automatic document feeder are simultaneously stopped, and the documents respectively placed at the exposure location and the resist unit are kept not to be discharged until this trouble is settled.
In a case that a trouble such as a jam has once occurred as described above, if it takes a long period of time to settle the trouble, the next document which has been prefed remains to stand for the long period of time while being formed into a loop. As a result, the document is put into the state in which it naturally curls. If the document is transported as it is, a jam occurs, causing problems in that the normal document transportation is disabled and that the document is damaged.